Catheter based devices are used to treat a wide variety of medical problems in a minimally invasive manner. Catheters are used to place and expand angioplasty balloons used to widen veins and arteries narrowed by plaque. Small scaffolds called stents have been introduced into the vasculature using catheter-based systems in order to prevent the restenosis of such vessels. One of the problems that a catheter based device and system could be used to treat in a minimally invasive manner is mitral valve regurgitation, however, no commercially successful device for the treatment of mitral valve regurgitation in such a manner currently exists.
Mitral valve regurgitation is the backflow of blood from the left ventricle into the left atrium due to an improper alignment of the leaflets of the mitral valve thereby causing an imperfect closure of the valve. A gap between the anterior leaflet and posterior leaflet of the mitral valve is created by the improper closure providing a conduit for blood to flow through the mitral valve in a retrograde manner from the left ventricle to the left atrium. This gap may be a congenital defect or may be caused by disease, i.e., ischemic or idiopathic cardiomyopathy and/or intrinsic degenerative disease of components of the mitral valve apparatus. One type of condition, congestive heart failure (CHF), causes the heart to enlarge. In an enlarged heart the walls of the left ventricle are expanded or dilated which causes the papillary muscles to be displaced downward and/or outward resulting in a tethering of the chordae tendineae and subsequent tethering/pulling on the leaflets. Also, with CHF, the mitral annulus is dilated. The combination of the dilated annulus and the tethering on the leaflets prevents the leaflets from closing properly, thereby causing the problematic gap in the mitral valve. The resultant backflow through the mitral valve reduces the efficiency of the heart resulting in a need for the heart to beat faster and/or more forcefully in order to produce the same amount of blood flow. Mitral valve regurgitation may be asymptomatic in some patients but in other patients the reduction in blood flow and the resultant strain on the heart could result in arrhythmias, heart attack and possibly death.
The preferred current treatments for mitral valve regurgitation require open-heart surgery and/or the use of endoscopic techniques that are difficult for the surgeon and potentially dangerous for the patient. In one method of treatment, porcine heart valves or mechanical heart valves are used to replace the damaged or defective mitral valve. Such treatments require the use of open-heart surgery to accomplish the implantation. Such heterologous valves may be used in humans but often wear-out prematurely and additional open-heart surgery is required to replace such valves with additional heterologous or mechanical valves. Mechanical valves have been developed which may also be used as a replacement for a defective mitral valve, however, the implantation of a mechanical valve usually indicates long-term anti-coagulant therapy to prevent clots from developing around the valve that could lead to a dangerous embolism. Long-term anticoagulant treatment causes other problems such as unwanted internal and external bleeding and possibly strokes.
Another open-heart surgical procedure for treating functional mitral valve regurgitation is annuloplasty. In an annuloplasty procedure, a generally “D” shaped annuloplasty ring is implanted on the mitral valve annulus to reduce the size of the stretched mitral valve annulus, most importantly, the septal-lateral dimension and improve closing (or coaptation) of the valve thereby reducing regurgitation. The surgeon surgically attaches, i.e., sews, the annuloplasty ring to the mitral valve on the atrial side of the mitral valve. The annuloplasty ring is sewn to the annulus on a top portion (i.e., the atrial side) of the mitral valve. Once implanted, tissue generally grows over the annuloplasty ring, and a line of contact between the annuloplasty ring and the mitral valve will essentially enable the mitral valve to appear and function as a normal mitral valve by reestablishing coaptation of the mitral valve leaflets but the durability of the effect is variable and may decline within six months after the procedure. Although a patient who receives the annuloplasty ring may be subjected to anti-coagulant therapies, the therapies are not extensive, as a patient is only subjected to the therapies for a matter of weeks, e.g., until tissue grows over the annuloplasty ring.
A second open-heart surgical procedure used in the treatment of degenerative mitral valve regurgitation is the Alfieri stitch procedure which the uses an edge-to-edge suture in the mitral valve. An edge-to-edge stitch is used to stitch together an area at approximately the center of a gap defined between the anterior and posterior leaflets of the mitral valve. Once the stitch is in place, the stitch is pulled in to form a suture that holds the anterior leaflet against the posterior leaflet. By reducing the size of the gap between the anterior leaflet and the posterior leaflet, the amount of leakage through the mitral valve may be substantially reduced. Durability has been a concern for Alfieri procedures done without the addition of an annuloplasty ring. In addition, use of the edge-to-edge procedure is only indicated in certain degenerative pathologies where the primary abnormality or gap between the leaflets is centrally located.
Another method of treating mitral valve regurgitation is the implantation of a ventricular assist device. Such devices are expensive and difficult to implant and require the patient to use anti-coagulant therapy indefinitely. Long-term use of anti-coagulant therapy may result in unnecessary bleeding and strokes. Such ventricular assist devices are, therefore, indicated for use only in patients that would likely not survive without their use and are used to keep patients alive who are candidates for heart transplant surgery. Left ventricular assist devices are a “bridge” therapy rather than a final therapy.
While such invasive surgical procedures have under certain circumstances been shown to be effective in the treatment of mitral valve leakage, invasive surgical procedures often have significant drawbacks. Any time a patient undergoes open-heart surgery, there is a risk of infection. Opening the sternum and using a cardiopulmonary bypass machine has also been shown to result in a significant incidence of both short and long term neurological deficits.
Some minimally invasive procedures have been developed to treat mitral valve regurgitation but, to date, none have become commercially successful standard procedures. U.S. Pat. No. 6,619,291 to Hvlaka et al. discloses a minimally invasive method of performing annuloplasty including inserting an implant into a left ventricle and orienting the implant in the left ventricle substantially below the mitral valve. The implant and tissue around the mitral valve are connected and tension is provided to the implant in order to substantially reduce an arc length associated with the mitral valve.
In U.S. Pat. Nos. 6,718,985 and 7,037,334 to Hvalaka et al. a series of plications near the mitral valve are created by T-bars that are threaded together to reshape the mitral valve. In U.S. Pat. No. 7,166,127 a catheter based system for treatment of mitral valve regurgitation uses a retainers adapted to be secured to the annulus of the mitral valve with flexible tensile members coupled to the retainers. A crimping device deployable through the catheter compresses a crimp onto the flexible tensile members after they are pulled toward one another to reduce the circumferential length of the annulus. In this system the number of permanent implants required in order to achieve an initial effect, and commitment to these implants before success of effect is able to be determined are serious drawbacks.
In United States Patent Application Publication No. 2007/0093857, Rogers et al. describes a device and method for the treatment of mitral valve regurgitation using a minimally invasive procedure in which plications are made proximate the mitral valve of the patient and a retainer is placed to hold the plication.
United States Patent Application No. 2007/0032797 discloses a device for reducing the size of the stomach having a corkscrew-shaped anchor for placement in the gastric wall.
United States Patent Application No. 2007/0025737 to Messerly et al. discloses a surgical retainer having a generally helical shape and a device having jaws for grasping tissue into which the helical retainer may be driven.
United States Patent Application No. 2007/0055335 discloses an electrode probe having a corkscrew-shaped distal tip for use in cardiology applications.
The need remains for a device and method for treating mitral valve regurgitation that can be used efficiently and effectively in a minimally invasive procedure and that provides the physician with the ability to know that the procedure has resulted in the desired effect prior to removing the device from the patient thereby reducing the need for and expense of repeat procedures. Such a procedure should provide the physician with the ability to changes the effect on the mitral valve during the procedure before taking an irreversible action.